With the system closed or in normal operation mode, can you get pressure? Made sure the little holes in the bottom of the MC are clear and clean of gummed up stuff or old caked on bake fluid. My old go to method is vacuum on bottom nipple with a wrench on the nipple. Pump MC handle and hold it to the bar. Release the pressure with the wrench and the bleed nipple and see if there is fluid coming out going to the vacuum tube. There should be some movement. This will not happen very well if the MC is not clean to work as designed.